Grape::API::Instance.to_s returns "" since 3.0.0 (nil-guard lost when converted to def_delegators)

[sneako]

Grape::API::Instance.to_s returns "" instead of its own class name. name is still correct, so the two disagree — which breaks anything that renders a class by its string representation.

Regression introduced in 3.0.0, still present in 3.3.4 and on master.

Repro

require "bundler/inline"
gemfile(true, quiet: true) do
  source "https://rubygems.org"
  gem "grape", ENV.fetch("GRAPE_VERSION", "3.3.4")
end
require "grape"

class MyAPI < Grape::API
  get("/ping") { "pong" }
end

puts "Grape::API::Instance.name   #{Grape::API::Instance.name.inspect}"
puts "Grape::API::Instance.to_s   #{Grape::API::Instance.to_s.inspect}"
puts "MyAPI.base_instance.to_s    #{MyAPI.base_instance.to_s.inspect}"
puts "interpolated: 'class #{Grape::API::Instance}'"

grape 3.3.4 (ruby 3.4.5):

Grape::API::Instance.name   "Grape::API::Instance"
Grape::API::Instance.to_s   ""
MyAPI.base_instance.to_s    "MyAPI"
interpolated: 'class '

grape 2.3.0, same script:

Grape::API::Instance.name   "Grape::API::Instance"
Grape::API::Instance.to_s   "Grape::API::Instance"
MyAPI.base_instance.to_s    "MyAPI"
interpolated: 'class Grape::API::Instance'

Cause

lib/grape/api/instance.rb delegates to_s to @base:

def_delegators :@base, :to_s

@base is only assigned through base=, which runs when an API subclass builds its mount instance. On the bare Grape::API::Instance class it is never set, so the delegator evaluates nil.to_s and yields "".

Before 3.0.0 the same delegation existed as an explicit method with a nil guard:

def to_s
  base&.to_s || super
end

It was replaced in 3e46a25 ("Delegate to_s to base in instance"). The delegation itself is fine and clearly intended — note in the output above that MyAPI.base_instance.to_s returns "MyAPI" under both versions. The old form already produced that result; what the rewrite changed is only the nil case, where || super used to fall back to Module#to_s.

Impact

Any tooling that enumerates loaded classes and renders them by string representation gets an empty name. We hit this through Sorbet/Tapioca: a DSL compiler iterating all classes emitted an RBI containing a bare class with no name, which then failed to parse:

sorbet/rbi/dsl/grape/api/instance.rbi:12: unexpected token tNL

That was on a grape 2.3 → 3.3 upgrade, and it took a while to attribute because name is correct and only to_s is blank — the two disagreeing is what makes it surprising. It also degrades grape's own diagnostics, since anything interpolating the class into a message renders nothing.

Suggested fix

Restore the nil fallback while keeping the delegation behavior:

def to_s
  @base&.to_s || super
end

Happy to open a PR with a spec if you'd like.

[ericproulx]

@sneako I think it's still an issue.

[sneako]

@sneako I think it's still an issue.

Thanks @ericproulx, I think that's very likely.

I closed the issue because Claude opened it without me noticing, while it was working on something else. I wanted to make sure it was valid myself before letting it get on the radar of the maintainers.

Sorry about that!

[ericproulx]

@sneako all right :) I'm opening a PR as I write this, I mean AI is opening a PR 😆

[ericproulx]

@sneako done. I'll release a 3.4 this week. AI found several bugs and it deserves it's on minor.

[sneako]

Amazing, thank you!